It is known to use ultrasonic waves to inspect elongated objects such as bolts, studs and the like which are undergoing stress corrosion. Such tests identify flaws such as stress corrosion cracks or the like and thereby determine the end of the stud lifetime. Such cracks are generally oriented transversely to the axis of the workpiece, and hence the ultrasonic beam must be directed axially along the workpiece to detect the crack. Tests are conducted periodically, and of significant interest is the change in the condition of the workpiece from test to test.
For a comparison of successive test results to be meaningful, it is of course necessary that the position of the ultrasonic transducer on the workpiece and its contact pressure thereagainst be consistent from test to test.
However, prior to the present invention it was necessary to establish the transducer position and contact pressure by hand for each test. Using hand control, it was possible to recover the positioning and contact pressure of previous tests only with great difficulty, and even then, over a long period of time and still only within wide tolerances. For example, the maximum inspection time per workpiece was approximately two hours, and even then it was not possible to work within tolerances less than .+-.2.degree..
Hence, prior to the present invention, a need existed to provide consistent positioning and contact pressure of a testing transducer relative to a workpiece, especially in the case where successive readings must be compared with each other.
Prior U.S. Pat. Nos. 3,602,036; 3,640,123 and 4,084,444 relate to ultrasonic testing. However, in these patents the ultrasonic beams are directed transversely relative to an elongated workpiece as contrasted to the present invention which involves directing the beam axially along the elongated workpiece.
U.S. Pat. Nos. 3,218,845 and 3,552,190 relate to directing ultrasonic waves down the length of a workpiece. However, these do not relate to the problem of consistently repositioning a given transducer.